Method, Apparatus and System for Key Derivation

1. A base station functioning as a source base station for a user equipment (UE), comprising: a receiver configured to receive a measurement report from a UE; a processor configured to make a handover decision and to derive multiple keys corresponding to multiple cells of a target base station for the UE; and a transmitter configured to send a handover request message to the target base station for the UE, the handover request message comprising the multiple keys.

2. The base station according to claim 1 , wherein the multiple keys are derived according to physical cell identifiers (IDs) of cells of the target base station for the UE.

3. The base station according to claim 2 , wherein the multiple keys are derived according to the physical cell IDs of target base station cells having a priority equal to or greater than a predetermined threshold.

4. The base station according to claim 1 , wherein the multiple keys are all or part of keys of all cells of the target base station for the UE.

5. The base station according to claim 1 , wherein the receiver is further configured to receive a handover request Acknowledgement (ACK) message from the target base station for the UE.

6. A base station functioning as a target base station for a user equipment (UE), comprising: a receiver configured to receive a handover request message from a source base station for the UE, the handover request message comprising multiple keys corresponding to multiple cells of the target base station for the UE, and the receiver being further configured to receive a radio resource control (RRC) connection reestablishment request from the UE; and a processor configured to select a key from the multiple keys for using in communication with the UE, the selected key corresponding to a target cell that the UE requests to access.

7. The base station according to claim 6 , further comprising a transmitter configured to send a RRC connection reestablishment message to the UE in response to the RRC connection reestablishment request.

8. The base station according to claim 6 , further comprising a transmitter configured to send a handover request Acknowledgement (ACK) message to the source base station for the UE in response to the a handover request message.

9. The base station according to claim 6 , wherein the multiple keys are derived according to physical cell identifiers (IDs) of the cells of the target base station for the UE.

10. The base station according to claim 9 , wherein the multiple keys are derived according to the physical cell IDs of target base station cells having a priority equal to or greater than a predetermined threshold.

11. The base station according to claim 6 , wherein the multiple keys are all or part of keys of all cells of the target base station for the UE.

12. A communication system, comprising: a source base station for a User Equipment (UE) and a target base station for the UE, wherein: the source base station is configured to receive a measurement report from the UE, to make a handover decision, to derive multiple keys correspond to multiple cells of the target base station, and to send a handover request message carrying the multiple keys to the target base station; and the target base station is configured to receive the handover request message from the source base station, to receive a radio resource control (RRC) connection reestablishment request from the UE, and to select a key from the multiple keys for use in communication with the UE, the selected key corresponding to a target cell that the UE requests to access.

13. The communication system according to claim 12 , wherein the multiple keys are derived by the source base station according to physical cell identifiers (IDs) of cells of the target base station for the UE.

14. The communication system according to claim 12 , wherein the RRC connection reestablishment request comprises information of the physical cell ID of the target cell which the UE requests to access.

15. The communication system according to claim 12 , wherein the selected key is selected by the target base station according to a physical cell ID of a target cell.

16. The communication system according to claim 12 , wherein the target base station is further configured to send a RRC connection reestablishment message to the UE in response to the RRC connection reestablishment request.

17. The communication system according to claim 12 , wherein the target base station is further configured to send a handover request Acknowledgement (ACK) message to the source base station for the UE in response to the handover request message.

18. The communication system according to claim 12 , wherein the target base station is further configured to send a physical cell ID of the target cell to the UE.

19. A base station functioning as a source base station for a user equipment (UE), comprising: a receiver configured to receive a measurement report from a UE; a processor configured to make a handover decision and to derive multiple keys corresponding to multiple cells of a target base station for the UE; and a transmitter configured to send a handover request message to the target base station for the UE, the handover request message comprising the multiple keys, wherein the multiple keys are all or part of keys of all cells of the target base station for the UE, and the receiver is further configured to receive a handover request Acknowledgement (ACK) message from the target base station for the UE.

20. The base station according to claim 19 , wherein the multiple keys are derived according to physical cell identifiers (IDs) of cells of the target base station for the UE.

21. The base station according to claim 20 , wherein the multiple keys are derived according to the physical cell IDs of target base station cells having a priority equal to or greater than a predetermined threshold.